This invention relates to an electrostatographic printer or copier, and more particularly concerns a cleaning apparatus for removing toner from an imaging surface.
Electrostatic brush (ESB) cleaners are designed to satisfy a requirement of cleaning a maximum toner mass entering the cleaner in a given number of passes through the cleaner. Generally these requirements are a maximum single pass cleaning requirement and a maximum two pass cleaning requirement. The single pass cleaning requirement is typically a residual toner mass on a photoreceptor belt following transfer under conditions of the highest developed mass (DMA) with the lowest transfer efficiency (TE). In some machines a mark-to-edge, or bleed edge, requirement raises the single pass cleaning requirement to the highest DMA level. The two pass cleaning requirement is typically cleaning of untransferred control patches and/or untransferred images in jam recovery. These input densities are equal to the highest DMA. It has been demonstrated that a two pass cleaning requirement is equivalent to cleaning half of the required toner mass in a single pass.
The two pass cleaning requirement, except in the case of mark-to-edge machines, is much more stressful than the single pass cleaning requirement. Therefore, the cleaning brushes are designed to clean the two pass requirement. Half of the toner is cleaned in each pass through the cleaner. In designing the cleaner the speed of the brushes, the number of fibers on the brushes, the interference of the brushes to the photoreceptor belt, the electrical bias on the brushes and the number of brushes are chosen to clean the equivalent single pass toner input.
Conventional multiple electrostatic brush cleaners consist of two or more brushes electrically biased to remove toner and other debris from the photoreceptor surface of the photoreceptor belt. Prior to the brushes a preclean charge device adjusts the toner charge of the incoming toner to a natural tribo charging polarity of the toner. This is known as right sign toner. Toner that does not charge to the polarity of the majority of the toner in the preclean charging step is known as wrong sign toner. The first brushes are biased opposite to the polarity of the right sign toner so that this toner can be removed. The last cleaning brush is biased opposite to the first brushes so that the wrong sign toner can be removed. Since there is only a small percentage of the toner that is wrong sign only a single brush is ever needed to clean the wrong sign toner mass.
Conventional multiple electrostatic brush cleaners have their single pass toner cleaning capacity limited by the amount of right sign toner that can be cleaned by the first brushes and the amount of wrong sign toner that can be cleaned by the last brush. As more cleaning capacity is required, such as for an increase in machine process speed, additional right sign cleaning brushes or additional cleaning passes must be added. These additions to the cleaning system are undesirable. Additional cleaning brushes increase the size and cost of the cleaner and may not fit in the available machine space. Additional cleaning passes decrease the productivity of the machine by requiring a longer recovery from paper jams. Additional cleaning passes impact the xerographic control of the machine by requiring a longer time to clean process control patches.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 5,729,815 to Lindblad et al. discloses an apparatus and method for cleaning charged triboelectric negative toner residual particles from a photoreceptor surface. A positive bias is applied to two electrostatic brushes in a dual cleaning system or to a single electrostatic brush. The rotational speed of the single electrostatic brush is increased, over that of the individual brushes in a dual brush cleaner, to clean charged triboelectric negative toner particles.
U.S. Pat. No. 5,257,079 to Lange et al. discloses a cleaning brush electrically biased with an alternating current to remove discharged particles from an imaging surface. The particles on the imaging surface are discharged by a corona generating device. A second cleaning device including an insulative brush, a conductive brush or a blade, located upstream of the first mentioned brush, in the direction of movement of the imaging surface, further removes redeposited particles therefrom.
U.S. Pat. No. 4,545,669 to Hays et al. discloses an apparatus for simultaneously charging, exposing, and developing imaging members at low voltages which comprises a semi-transparent deflected flexible imaging member, an electronic imaging source means, a light beam deflector member, a means containing magnets therein, a development roll means containing magnets therein, a voltage source means for sensitizing roll means, a voltage source for the development roll means, a developer supply reservoir containing conductive developer particles therein comprised of insulating toner resin particles and conductive carrier particles, a sensitizing nip situated between the flexible imaging member and the sensitizing roll means, a development nip situated between the flexible imaging member and the development roll means, the sensitizing roll means and development roll means moving in the same direction of movement as the semitransparent deflected flexible imaging member, the voltage being generated by the voltage source means with the sensitizing nip being of an opposite polarity of the voltage generated by the voltage source means for the development roll means, wherein an electric field of a predetermined polarity is established between the semi-transparent deflected flexible imaging member and the sensitizing roll means, which field exerts in the sensitizing nip an electrostatic force on the charged toner particles causing these particles to uniformly migrate toward the flexible imaging member, subsequently subjecting the deflected flexible imaging member to the electronic imaging source means whereby the electrostatic force exerted on the toner particles adjacent the light struck areas of the flexible imaging member are increased thereby causing toner particles to be deposited on the deflected flexible imaging member, and wherein toner particles are removed from the deflected flexible imaging member in areas not exposed to light by the development roll means and developed in the areas exposed to light.
Briefly stated, and in accordance with one aspect of the present invention, there is provided a multiple electrostatic brush cleaner the first brushes are biased to clean right sign toner and the last brush is biased to clean wrong sign toner. The highest cleaning stress occurs when untransferred toner is cleaned following a machine jam or control patches are cleaned. Generally two or more passes are allowed to clean these very high density inputs to the cleaner. The present invention biases all brushes for the first cleaning pass to clean right sign toner. On the second cleaning pass the brushes are biased normally. This new bias switching arrangement results in more efficient use of the cleaning brushes and allows existing cleaners to be used at higher process speeds than with conventional multi-pass cleaner biasing. Bias switching is especially advantaged with air detoning of the electrostatic brush cleaner since little toner accumulates in the brushes. Since there are opportunities for any toner redeveloped to a photoreceptor during the bias switching to be cleaned in the following passes, switching may also be useful in electrostatically detoned cleaners.